The present invention relates to electronic components and construction, and pertains particularly to an improved coil and method of manufacturing.
For many years, electronic circuit boards have been fabricated by interconnecting a plurality of electronic components, both active and passive, on a planar printed circuit board. Typically, this printed circuit board has comprised an Epoxy/fiberglass laminate substrate clad with a sheet of copper, which has been etched to delineate the conductive paths. Holes were drilled through terminal portions of the conductive paths for receiving electronic component leads, which were subsequently soldered thereto.
More recently, so-called surface mount technology has evolved to permit more efficient automatic mass production of circuit boards with higher component densities. With this approach, certain packaged components are automatically placed at preselected locations on top of a printed circuit board, so that their leads are registered with, and lie on top of corresponding solder paths or pads. The printed circuit board is then processed by exposure to infrared or vapor phase soldering techniques to re-flow the solder, and thereby establish a permanent electrical connection between the leads and their corresponding conductive paths on the printed circuit board.
The increasing miniaturization of electrical and electronic elements and high density mounting thereof has created increasing problems with construction of electrical components as well as electrical isolation and mechanical interconnection. Demand for even greater miniaturization increase the need for better and more efficient components and techniques of construction. In particular, it creates more difficulty in providing adequate power from smaller components and establishing reliable and efficient connection between packaged components and terminals. Presently known construction and interconnect methods severely limit the ability to provide more compact and powerful components and high density and reliable components and electrical and mechanical isolation between components distinct terminal points due to space limitations.
Among the electrical and electronic elements that must be made more compact and efficient and surface mounted on PC boards are coils, such as transformers, inductors and the like. These must be constructed to be low profile, be high powered and efficient.
The current technique of construction of transformers and other coils is to wind round or square copper wires on a somewhat flat bobbin or pole piece. Layers of tape are wrapped between the layers of wire to provide high voltage insulation. A problem with round wire is that at high frequencies, the current penetrates only a small depth, called skin depth, on the wire surface. To overcome this, some manufactures have used a bundle of small wires, called litz wire. This provides more surface area, but a large portion of the cross-sectional area is unused because of the space between the wires. This is an inefficient use of the space taken up by the bundle of wires.
Conductive tapes have been proposed to reduce the above density problem. A conductive tape is wound alternately with an insulating tape on a conventional bobbin, with round wires soldered at the ends of the tape for terminal lead connections. However, this terminal lead structure adds thickness to the assembly and defeats efforts to miniaturize the transformer. For example, a 20 mil wire soldered to a 2.5 mil tape will typically result in a 30 mil thickness.
Another approach to miniaturization has been to go to a planar magnetic transformer. This structure has a circuit board type construction wherein sheets of conductive plates are formed with a center hole wherein the core extends perpendicular to the surface of the plates or circuit boards. Leads for the planar magnetic construction extend down through holes in the printed circuit boards. This provides a low profile, but is expensive and low powered.
It is, therefore, desirable that an improved transformer construction with high power, low profile and with improved lead form for termination and surface mounting be available.